1. Field of the Invention
The present invention relates to uses and applications for diamond. More particularly, the present invention relates to applications and uses of single-crystal diamond produced at a high growth rate using Microwave Plasma Chemical Vapor Deposition (MPCVD) within a deposition chamber.
2. Description of Related Art
Large-scale production of synthetic diamond has long been an objective of both research and industry. Diamond, in addition to its gem properties, is the hardest known material, has the highest known thermal conductivity, and is transparent to a wide variety of electromagnetic radiation. Monocrystalline diamond in particular possess a wide range of important properties, including a low coefficient of thermal expansion, the highest known thermal conductivity, chemical inertness, wear resistance, low friction, and optical transparency from the ultra-violet (UV) to the far infrared (IR). Therefore, it is valuable because of its wide range of applications in a number of industries and research applications, in addition to its value as a gemstone.
For at least the last twenty years, a process of producing small quantities of diamond by chemical vapor deposition (CVD) has been available. As reported by B. V. Spitsyn et al. in “Vapor Growth of Diamond on Diamond and Other Surfaces,” Journal of Crystal Growth, vol. 52, pp. 219-226, the process involves CVD of diamond on a substrate by using a combination of methane, or another simple hydrocarbon gas, and hydrogen gas at reduced pressures and temperatures of 800-1200° C. The inclusion of hydrogen gas prevents the formation of graphite as the diamond nucleates and grows. Growth rates of up to 1 μm/hour have been reported with this technique.
Subsequent work, for example, that of Kamo et al. as reported in “Diamond Synthesis from Gas Phase in Microwave Plasma,” Journal of Crystal Growth, vol. 62, pp. 642-644, demonstrated the use of Microwave Plasma Chemical Vapor Deposition (MPCVD) to produce diamond at pressures of 1-8 kPa at temperatures of 800-1000° C. with microwave power of 300-700 W at a frequency of 2.45 GHz. A concentration of 1-3% methane gas was used in the process of Kamo et al. Maximum growth rates of 3 μm/hour have been reported using this MPCVD process. In the above-described processes, and in a number of other reported processes, the growth rates are limited to only a few micrometers per hour.
Methods of improving the growth rates of single-crystal chemical vapor deposition (SC-CVD) diamonds have recently been reported [1, 2, 3, 4, 5]. SC-CVD diamonds reported so far, however, are relatively small, are discolored, and/or are flawed. Large (e.g., over three carats, as commercially available high pressure, high temperature (HPHT) synthetic Ib yellow diamond), colorless, flawless synthetic diamonds remain a challenge due to slow growth and other technical difficulties [7, 8, 9]. The color of SC-CVD diamonds in the absence of HPHT annealing can range from light brown to dark brown, thus limiting their applicability as gems, in optics, in scientific research, and in diamond-based electronics [6, 7, 8]. SC-CVD diamonds have been characterized as type IIa, i.e., possessing less than 10 ppm nitrogen, and have coloration and other optical properties arising from various defects and/or impurities.
A diamond crystal of 10 carats is approximately five times that of commercially available HPHT diamond and the SC-CVD diamond reported in References [7, 8, 9, 10]. Single-crystal diamonds with larger mass (greater than 100 carats) are needed as anvils for high-pressure research, and crystals with large lateral dimensions (greater than 2.5 cm) are required for applications such as laser windows and substrates for diamond-based electronic devices. High optical quality (UV-visible-IR transmission) and chemical purity are required for all of the above applications. The large SC-CVD diamonds produced so far present problems because of the brownish color.
Attempts have been made to add oxygen in the growth of polycrystalline CVD diamond. These effects include extending the region of diamond formation [12], reducing silicon and hydrogen impurity levels [13], preferentially etching the non-diamond carbon [11, 14], and attempting to prevent diamond cracks due to an absence of impurities [13]. These attempts were directed primarily to the etching and synthesis of polycrystalline diamonds but not to the production of SC-CVD diamond.
Attempts have also been made to intentionally vary the color of the single-crystal diamond formed. Yellow diamonds, for instance, have been produced that are similar to HPHT synthetic Ia or Ib diamond in appearance [6].
U.S. Pat. No. 6,858,078 to Hemley et al. is directed to an apparatus and method for diamond production. The disclosed apparatus and method can lead to the production of diamonds with a light brown color.
U.S. Provisional Application No. 60/684,168, filed May 25, 2005, which is hereby incorporated in its entirety by reference, is directed to producing colorless, single-crystal diamonds at rapid growth rate using Microwave Plasma Chemical Vapor Deposition (MPCVD) within a deposition chamber.
Until now, few attempts have been made to develop products which use single-crystal diamonds produced by MPCVD. Moreover, few attempts have been made to develop uses and applications for single-crystal diamonds that are not doped with impurities.
Thus, there remains a need to develop new uses and applications for colorless, single-crystal diamonds produced at a rapid growth rate. There also remains a need to develop new uses and applications for single-crystal diamonds of varying color grown at a rapid growth rate.